The present invention relates to a vehicular air-conditioner that has a variable displacement compressor in a refrigerant circuit. The compressor is driven by a vehicular power source such as an internal combustion engine to compress refrigerant gas and is also driven by an electric motor to compress refrigerant gas when the internal combustion engine is not running.
Recently, an idling stop system is becoming widely used to improve the fuel economy and for environmental protection. The idling stop system stops the engine when a vehicle is stopped at stoplights. A compressor, which has an electric motor as a drive source, has been proposed to enable the air conditioning of a passenger compartment while the engine is not running.
An electric motor having the same driving performance as the engine is large and does not fit in the engine room. Therefore, the electric motor to be provided in the compressor needs to be small. However, a small electric motor may cause a power swing due to an excessive compressor torque, particularly at the activation of the motor. When the electric motor causes a power swing, the electric motor stops and might hinder the air conditioning performance.
Japanese Laid-Open Patent Publication No. 10-236151 discloses such an air conditioning system. The disclosed air conditioning system employs a variable displacement compressor. Before actuating the compressor with an electric motor, the displacement of the compressor is minimized. Therefore, when the motor is activated, the compressor torque is small. Thus, the motor is reliably activated.
However, even after the motor is activated, or in a case where the motor is unlikely to cause power swing as compared to when the motor is being activated, the displacement of the compressor is maintained at the minimum. To drive the motor in a stable manner at the same time as performing the air conditioning in a suitable manner, the displacement of the compressor needs to be changed (increased) within the range that can be managed by the output of a small motor.
In a typical variable displacement compressor, the displacement is decreased when the pressure in a crank chamber is large and the displacement is increased when the pressure in the crank chamber is small. The compressor is provided with a control valve for adjusting the pressure in the crank chamber to vary the displacement. The control valve is, for example, located in a supply passage that connects the discharge chamber to the crank chamber. The control valve includes a bellows and an electromagnetic solenoid. The bellows moves a valve body in accordance with the pressure in the suction chamber (suction pressure). The electromagnetic solenoid applies force to the valve body based on external conditions, such as the temperature in the passenger compartment. The force that the solenoid applies to the valve body reflects the target value of the suction pressure (target suction pressure).
An operation for decreasing the temperature in the passenger compartment will now be described. A controller computes the target suction pressure based on the information from several sensors to decrease the detected room temperature to a desired temperature. The controller commands a drive circuit to supply current to the electromagnetic solenoid based on the computed result to decrease the opening degree of the valve body. The commands of the controller constitute commands externally to the electromagnetic solenoid. When the opening degree of the valve body is decreased, the amount of refrigerant supplied to the crank chamber through the supply passage from the discharge chamber decreases. Accordingly the crank pressure is decreased, which increases the displacement of the compressor. As a result, the cooling performance is increased and the temperature in the passenger compartment decreases toward the desired temperature. Accordingly, the actual suction pressure decreases toward the target suction pressure.
The bellows moves the valve body in accordance with the actual suction pressure such that the actual suction pressure seeks the target suction pressure. For example, when the suction pressure is greater than the target suction pressure, the bellows decreases the opening degree of the valve body. Therefore, as described above, the displacement of the compressor increases, which decreases the suction pressure toward the target suction pressure.
To reliably activate the motor, the control valve maintains the valve body at the fully opened position when the solenoid is demagnetized, and the displacement of the compressor is minimized.
However, the bellows of the control valve is automatically controlled based on the fluctuation of the suction pressure. Therefore, when the target suction pressure is changed by the solenoid, the movement of the bellows differs depending on the actual suction pressure at the time the target suction pressure is changed. The displacement of the compressor is changed in different manner based on the difference in the movement of the bellows.
More specifically, the compressor is stopped when the power source of the compressor is switched from the engine to the motor. When the compressor is stopped, the suction pressure excessively increases. Thus, even though the target pressure is set relatively high by the solenoid after the motor is activated, the bellows rapidly decreases the opening degree of the valve body to decrease the excessive actual suction pressure to the target suction pressure. As a result, the displacement of the compressor rapidly and excessively increases, which hinders the reliable activation of the motor.
The above described problem is caused not only in the case with the variable target suction pressure valve but in all types of control valves combining the pressure sensing mechanism and the electromagnetic actuator.
Accordingly, it is an objective of the present invention to provide a vehicular air-conditioner that stabilizes the operation of an electric motor and performs air conditioning in a suitable manner at the same time when actuating a variable displacement compressor by an electric motor.
In order to achieve the above objective, the present invention provides an air conditioning system for a vehicle that is driven by a vehicle engine, said system has a compressor selectively operable by the vehicle engine and an electric motor outputting a force smaller than that of the vehicle engine, said electric motor being used as a drive force of the compressor when the vehicle engine is in a non-operative state, wherein said compressor compresses refrigerant gas introduced into a suction chamber from an external refrigerant circuit, wherein a displacement of the compressor is variable based on a differential pressure between the compression chamber and a crank chamber, wherein the compressor has a control valve that is disposed on a refrigerant passage communicating with the crank chamber, wherein said control valve has a valve plunger for changing an opening size of the control valve to adjust pressure in the crank chamber, said system comprising:
pressure sensing member disposed in the control valve and applying biasing force to the plunger based on pressure in the external circuit, wherein the biasing force is applied to cancel change of the pressure in the external circuit;
actuator disposed in the control valve and applying reverse force against the biasing force to the plunger, wherein the plunger is moved to increase the displacement by the reverse force; and
controller for controlling the actuator to stepwise increase the reverse force by a magnitude at which the electric motor is able to stably drive the compressor.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.